When a scientific field is well-established and has reached the status of what Thomas Kuhn once called a 'paradigm,' it usually takes a 'scientific revolution' to elicit what eventually turns out to be a Kuhnian 'paradigm shift'--a move away from the old theory and its replacement by a new one which is developed and defended by a new generation of scholars. One thing that can prompt such a revolution is the discovery of a fair amount of new and (initially) puzzling empirical data that cannot be accommodated by the old theory or some straightforward variant of it but rather require a completely new approach. Another possibility, however, is that the revolution starts not bottom-up, but top-down, i.e., is prompted by a conceptual criticism of the theories, concepts, and methods characteristic of the old paradigm.

Massimo Pigliucci and Jonathan Kaplan's Making Sense of Evolution: The Conceptual Foundations of Evolutionary Biology certainly belongs to the latter category, even if it eventually turns out in a few years that it didn't revolutionize the field--evolutionary biology, or more precisely, quantitative genetics, in that case--but only triggered a serious reconsideration of some of the core concepts, methods and theories of what seemed to be a completed field of investigation at the end of the twentieth century. Massimo Pigliucci is professor of ecology and evolution at SUNY Stony Brook, and his co-author Jonathan Kaplan is professor of philosophy at Oregon State University. In their book, they are criticizing so-called 'Neo-Darwinism', the 'Modern Synthesis' of genetics and evolutionary theory that has held sway since it was launched by Fisher, Haldane and Wright in the 1940s and then made prominent by people like Mayr and Dobzhansky. Pigliucci and Kaplan's goal is to critically examine the logic, consistency and applicability of some of the fundamental concepts that are usually more or less uncritically employed in 'mainstream' evolutionary biology, including such basic concepts as 'natural selection,' 'genetic drift,' and 'fitness' (chs. 1 and 2), 'adaptation' (ch. 5), 'function (ch. 6), or 'species' (ch. 9), more specialized notions such as the concept of an 'adaptive landscape' (ch. 8) or the idea of 'genetic constraints' (ch. 4), and issues that have been hotly debated in the past in biology and the philosophy of biology, like 'units of selection' (ch. 3) or the possibility of 'testing evolutionary hypotheses' (ch. 10).

According to Pigliucci and Kaplan, some of the well-entrenched core ideas in evolutionary biology, including the ones just mentioned, are deeply problematic. Either they can be construed in a variety of not obviously compatible ways, or they fit rather badly with what evolutionary biologists are actually doing in the course of their empirical research. Consider, to take just one particularly important example, the notion of fitness that plays an indispensable role in the formulation of evolutionary theory. In ch. 1 Pigliucci and Kaplan argue that there are at least two incommensurable notions of fitness in use in evolutionary theory (in particular in evolutionary genetics). On the one hand a notion of formal fitness as a statistical, and measurable, abstract property of populations (i.e., fitness as average reproductive success) and on the other hand a notion of informal fitness that concerns causal processes relevant to particular traits of individuals in populations. What Pigliucci and Kaplan try to show is that few biologists are aware of the consequences of the attempt to connect individual-level natural selection with natural selection (the same concept!?) at the level of populations. At the core of their of their criticism is a thorough philosophical reflection on how statistical and causal analyses are related to one another, especially the difficulty of inferring underlying (in this case biological) mechanisms from statistical patterns. The idea that correlation is not causation, and that it is difficult to establish causal claims on the basis of correlations alone, is rather well-known in philosophy of science and certainly nothing new. What is new, however, is the use Pigliucci and Kaplan make of this as such simple fact in their criticism of the traditional use of the notion of 'natural selection' and other important concepts in evolutionary biology. Chapter by chapter, they show that what is taken for granted both by theorists in the field and by practicing biologists is actually far from clear. The message throughout is: The conceptual foundations of evolutionary biology are in (a totally unexpected) disarray.

One word of caution may be appropriate. The subtitle of the book -- The Conceptual Foundations of Evolutionary Biology -- may be read as suggesting that the reader of the who is unacquainted with evolutionary biology can, by reading the book, acquired some first understanding of the core notions of evolutionary biology. Readers with this expectation will be disappointed. It's not that Pigliucci and Kaplan's book is a bad one. Far from it. But its value can be appreciated only by those few researchers who are as deeply into the matter as Pigliucci and Kaplan themselves. Making Sense of Evolution is a good book, a terrific book indeed, but it is also a terribly complicated book that requires a lot of background in biology, philosophy of science and mathematical modeling. To the uninitiated, it is useless. To the expert, it is immensely valuable, and I am sure it will shape discussions about the theoretical foundations in evolutionary theory for the years to come.

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